One well known way to increase the performance of hard disk drives is to increase the areal data storage density of the magnetic hard disk. This can be accomplished by reducing the written data track width, such that more tracks per inch can be written on the disk. To read data from a disk with a reduced track width, it is also necessary to develop sufficiently narrow read head components, such that unwanted magnetic field interference from adjacent data tracks is substantially eliminated.
The standard prior art read head elements include a plurality of thin film layers that are deposited and fabricated to produce a GMR read head, as is known to those skilled in the art. Significantly, where the width of the thin film layers that comprise the GMR read head is reduced below certain values, the magnetic properties of the layers are substantially compromised. To overcome this problem, GMR read heads have been developed in which the thin film layers have an ample width and the electrical leads are overlaid on top of portions of the thin film layers. This lead overlaid configuration has the effect of creating an active read head region having a width that is less than the entire width of the deposited layers, such that the magnetic properties of the thin film layers can be preserved. Thus, in the lead overlaid GMR read heads of the prior art, active magnetic layer portions exist between the electrical leads and passive magnetic layer portions exist beneath the electrical leads.
A problem that has been recognized with regard to such prior art lead overlaid read heads is that the passive region of the magnetic layers of the read head, and particularly the free magnetic layer, is not entirely passive. That is, external magnetic fields, such as from adjacent data tracks, create magnetic field fluctuation and noise within the passive regions of the free magnetic layer beneath the electrical leads. Thus, noise and side reading effects continue to be a problem with lead overlaid GMR read heads.
FIG. 1 is a side cross-sectional view of a prior art electrical lead overlaid read head portion of a magnetic head 100. As depicted therein, the prior art lead overlaid read head generally includes a substrate base 102 that constitutes the material from which the magnetic head is fabricated, such as aluminum titanium carbide. A first magnetic shield 104 is fabricated on the substrate, and an insulation layer 106, typically composed of aluminum oxide, is fabricated upon the magnetic shield 104. A seed layer 108 is deposited upon the insulation layer 106 and a series of thin film layers are sequentially deposited upon the seed layer 108 to form a GMR read head. In this structure, the layers generally include an antiferromagnetic layer 114, a pinned magnetic layer 118 that is deposited upon the anti ferromagnetic layer 114, a spacer layer 122 that is deposited upon the pinned magnetic layer 118, a free magnetic layer 126 that is deposited upon the spacer layer 122 and a cap layer 130 that is deposited upon the free magnetic layer 126. Typically, the antiferromagnetic layer 114 may be composed of PtMn, the pinned magnetic layer 118 may be composed of CoFe, the spacer layer 122 may be composed of Cu, the free magnetic layer 126 may be composed of CoFe and the cap layer 130 may be composed of Ta.
Following the deposition of the GMR read head layers 114-130, a patterned etching process is conducted such that only central regions 140 of the layers 114-130 remain. Thereafter, hard bias elements 148 are deposited on each side of the central regions 140. Following the deposition of the hard bias elements 148, electrical lead elements 154 are fabricated on top of the hard bias elements 148. As depicted in FIG. 1, inner ends 156 of the leads 154 are overlaid on top of outer portions 160 of the layers 114-130 of the central read head layer regions 140. A second insulation layer 164 is fabricated on top of the electrical leads 154 and cap layer 130, followed by the fabrication of a second magnetic shield (not shown) and further components that are well known to those skilled in the art for fabricating a complete magnetic head.
A significant feature of the prior art lead overlaid GMR read head depicted in FIG. 1 is that the portion of the central layer region 140 which substantially defines the track reading width W of the read head 100 is the central portion 144 of the read head layer regions 140 that is disposed between the inner ends 156 of the electrical leads 154. That is, because the electrical current flows through the read head layers between the electrical leads 154, the active portion 144 of the read head layers comprises the width w between the inner ends 156 of the electrical leads 154. The outer portions 160 of the read head layers disposed beneath the overlaid inner ends 156 of the electrical leads 154 are somewhat passive in that electrical current between the electrical leads 154 does not pass through them.
A significant problem with the prior art lead overlaid read head 100 depicted in FIG. 1 is that the magnetization in the outer portions 160 of the free layer 126 beneath the electrical leads 154 is unstable and subject to unwanted magnetic field fluctuations. Additionally, side reading effects from adjacent data tracks as well as magnetic noise is created in the passive portions 160 of the free layer 126 beneath the electrical lead ends 156. Thus, noise and side reading effects continue to be a problem with lead overlaid GMR read heads.
Further, prior art heads have hard bias material on either side of the sensor to exert magnetic force on the free layer to magnetically stabilize the free layer. The problem is that hard bias layers are very thick, and as track sizes shrink, sensors must get smaller. When the track width becomes very narrow, the hard bias layers makes the free layer very insensitive and thus less effective. What was needed was a way to create a sensor with a narrow track width, yet with a free layer that is very sensitive.
To overcome the problems described above, some heads are now constructed such that the magnetization of the free magnetic layer is pinned in the passive regions beneath the overlaid electrical leads, thus stabilizing the passive regions, and reducing noise and side reading effects.
FIG. 2 depicts another prior art lead overlaid read head 200. As depicted therein, the read head 200 includes a GMR read head thin film element 240, as well as the hard bias elements 248. As depicted therein, the prior art lead overlaid read head generally includes a substrate base 202 that constitutes the material from which the magnetic head is fabricated, such as aluminum titanium carbide. A first magnetic shield 204 is fabricated on the substrate, and an insulation layer 206, typically composed of aluminum oxide, is fabricated upon the magnetic shield 204. A seed layer 208 is deposited upon the insulation layer 206 and a series of thin film layers are sequentially deposited upon the seed layer 208 to form a GMR read head. In this structure, the layers generally include an antiferromagnetic layer 214, a pinned magnetic layer 218 that is deposited upon the anti ferromagnetic layer 214, a spacer layer 222 that is deposited upon the pinned magnetic layer 218, a free magnetic layer 226 that is deposited upon the spacer layer 222 and a cap layer 230 that is deposited upon the free magnetic layer 226.
This read head 200 includes an additional magnetic thin film layer 270 that is deposited on top of the hard bias elements 248, such that an inner portion 210 of the layer 270 extends over the outer portions 260 of the layers that comprise the read head element 240. The magnetic layer 270 is deposited on top of the outer portions 260 of the tantalum cap layer 230, and directly on top of the magnetic hard bias elements 248. The electrical leads 254 are thereafter fabricated on top of the magnetic layer 270.
Following the magnetic field initialization of the hard bias elements 248, the magnetic field of the hard bias elements 248 will create corresponding magnetic fields within the magnetic layer 270. Furthermore, because the inner portion 210 of the magnetic layer 270 is deposited on top of the outer portion 260 of the tantalum cap layer 230, which is deposited above the outer portion 260 of the free layer 226, the magnetic field within the inner portion 210 of the magnetic layer 270 will become magnetostatically coupled to the outer portion 260 of the free layer 226 through the tantalum cap layer 230. This provides a pinning effect upon the magnetic fields within the outer portion 260 of the free layer, because it raises the coercivity of the free layer within the outer region 260.
One problem encountered during manufacture of a lead overlaid read head is that when plating this kind of sensor, layer 226 is deposited, then layer 230 is deposited, then layer 270 is deposited as a contiguous layer. Then the portion of magnetic layer 270 in the central portion 244 of the read head layer regions 240 must be etched off without breaking through the cap layer 230. Some prior art processes use the cap layer 230 as a marker indicating when to stop etching. However, this layer 230 is typically only ˜8 angstroms or less, so there is danger of etching through the layer 230 and into the free layer 226.
Another drawback is that the prior art read heads 100,200 of FIGS. 1-2 require hard bias elements 148, 248. As track sizes shrink, sensors must get smaller. The smaller the sensor becomes, the more susceptible it is to interference from the hard bias elements 148, 248. When the track width becomes very narrow, the hard bias elements 148, 248 make the free layer very insensitive and thus less effective.
Another prior art method of creating heads with the magnetic moment of the free layer pinned in the outer regions is to oxidize the section of the magnetic layer in the active area. This makes the material nonmagnetic and thus inactive. FIG. 3 illustrates a lead overlaid read head 300 according to one preferred embodiment. As shown, the read head 300 includes a substrate base 302, a first magnetic shield 304 fabricated on the substrate, and an insulation layer 306 fabricated upon the magnetic shield 304. A seed layer 308 is deposited upon the insulation layer 306 and a series of thin film layers are sequentially deposited upon the seed layer 308 to form a GMR read head. In the preferred embodiment of the present invention, the layers generally include an antiferromagnetic layer 310, a lower pinned layer 312, a first spacer layer 314, a free magnetic layer 318 that is deposited upon the first spacer layer 314, a second spacer layer 322 that is deposited upon the free layer 318, a bias magnetic layer 326 that is deposited upon the second spacer layer 322 and a cap layer 330 that is deposited upon the bias layer 326. The magnetic moments of the free and bias layers are antiparallel.
The section of the magnetic layer is oxidized in the active area 344. The problem encountered here is that the second spacer layer 322 separating the free layer 318 and the bias magnetic layer 326 is typically 8 angstroms or less, so some of the oxidizing material can migrate through the second spacer layer 322, reaching the free layer 318 and oxidizing it. The oxidation in turn affects the signal quality achievable from the free layer 318.
In addition, because the second spacer layer 322 is crystalline, during thermal cycling of the head, and because of the heat generated during use, oxygen can diffuse through the second spacer layer 322 and oxidize the free layer 318, reducing its effectiveness.
What is needed is a way to form a sensor structure having antiparallel tab regions without excessive and dangerous processing on the active region of the sensor.